1. Field of the Invention
This invention relates to rotary body control apparatuses for controlling the speed and phase of the rotary body and, more particularly, to a rotary body control apparatus of the type which is quick in starting and which can easily phase lock-in with a reference phase signal.
2. Description of the Prior Art
Suppose that a voltage E.sub.o so as to flow a maximum allowable current is applied to a rotary body such as d.c. motors, to which a load having a sufficiently great inertia efficiency, for example, a load such as a magnetic disc, is fixed, the starting characteristic is shaped in the curve close to the primary delay element as shown in FIG. 1(a) and is finally shaped to be a constant speed S.sub.o in a fairly long time. However, normally a control apparatus is added to the rotary body so that operation is performed at a speed S.sub.1 lower than S.sub.o in a synchronous relation with a reference phase.
In control of the phase as described, if the accuracy of the phase synchronization is demanded, it is required to increase gain in a phase control system so that great torque is developed with respect to a fine deviation of the phase. With this construction, however, the greater phase deviation displaces a linear region in the phase contorl system, resulting in the lock-in of the phase synchronization being not assured.
The difficulty of the phase-lock in a phase control system having a high gain is additionally caused by the fact that when a phase of a phase signal from the rotary body is considerably displaced from a reference phase even if the speed of the rotary body is a predetermined speed, a great erroneous signal is detected so that voltage applied to the rotary body is fluctuated, resulting in the speed maintained at a predetermined rate as described hereinbefore being put into disorder, thus not assuring the phase lock. Further, if the phase synchronization is normally effective after the rotary body has been started, the lock-in would probably fail and the rising would also be inadequate. For this reason, it has been designed so that normally only speed contrl is performed until the speed of the rotary body reaches a required value after it is started, thereafter the phase control is also performed. According to the conventional procedure, however, the speed has been determined independently of frequencies of the reference phase signal, which lacks in stability. Moreover, if both speed control and phase control are carried out at speeds in the range required as described above, the rising characteristic would has been grown worse as shown in the dotted line in FIG. 1(c).